How does stimulus rise time relate to the S-parameter measurements with IConnect?

How does stimulus rise time relate to the S-parameter measurements with IConnect?

When the Time Domain Vector Network Analysis (TDVNA) is performed; a step signal is applied to analyze the DUT. The resulting response is then measured with the instrument and converted to the frequency domain with the help of IConnect in the form of S-parameters. The frequency range of the measured data is directly related to the signal rise time. Generally speaking, the faster the rise time the more frequency content is of the S-parameter response. If the rise time at the probe tip was 35ps one would expect an accurate S-parameter measurement at least up to 10GHz. The test measurements of S-parameters performed with IConnect indicate good correlation between the TDVNA and VNA setups up to 12 GHz.

When the higher frequency range is desired, a higher speed pulse source is needed. One of the simple solutions available on the market is a source enhancement module by PicoSecond Pulse Labs, which allows generating 9ps rise time extending the frequency range to more than 40GHz.